<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
    <title>3.9 移动端常用单位</title>
    <link rel="stylesheet" href="css/iconfont.css">
    <style>
        /*px/%/em/rem/vw/vh*/

        /*css reset*/
            * {
                box-sizing: border-box;
                padding: 0;
                margin: 0;
            }
            body {
                background-color: #e2e2e2;
                color: #595B66;
            }
            a {
                font-size: 12px;
                color: #686868;
                text-decoration: none;
            }
            li {
                list-style: none;
            }

        /*body {
            font-size: 20px;
        }*/

        html {
            font-size: 12px;
        }
        .tabbar-container {
            position: fixed;
            left: 0;
            bottom: 0;
            z-index: 1000;
            width: 100%;
            
            /*height: 5em;
            font-size: 12px;*/
            /*font-size: 12em;*/

            /*height: 5rem;*/

            /*width: 100vw;
            height: 10vh;*/
            background-color: #fff;
            box-shadow: 0 0 10px 0 rgba(154, 141 ,141, 0.6);

            height: 50px;
            /*
                height
                    375px -> 100%(375px) x 50px
                    750px -> 100%(750px) x 100px
                    ?(视口宽度) -> (? / 750) * 100 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    height = (document.documentElement.clientWidth / 750) * 100 px
                    height = (document.documentElement.clientWidth / 375) * 50 px
            */

            /*
                用px/em做单位，每次都要用js一一修改
                能不能统一修改呢？
                    375px -> 1rem = 20px;
                        height = 50 / 20 = 2.5rem;
                    750px -> 1rem = 40px;
                        height = 100 / 40 = 2.5rem;
                    ?(视口宽度) -> 1rem = (? / 375) * 20 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    1rem = (document.documentElement.clientWidth / 375) * 20 px
                    1rem = (document.documentElement.clientWidth / 750) * 40 px
                    height = 2.5rem;
            */
            /*375px 1rem = 20px;*/
            height: 2.5rem;
        }
        .tabbar-link .iconfont {
            /*font-size: 24px;*/
            font-size: 1.2rem;
            /*font-size: 2em;*/

            /*
                font-size
                    375px -> 24px
                    750px -> 48px
                    ?(视口宽度) -> (? / 750) * 48 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    font-size = (document.documentElement.clientWidth / 750) * 48 px
                    font-size = (document.documentElement.clientWidth / 375) * 24 px
            */
            /*
                用px/em做单位，每次都要用js一一修改
                能不能统一修改呢？
                    375px -> 1rem = 20px;
                        font-size = 24 / 20 = 1.2rem;
                    750px -> 1rem = 40px;
                        font-size = 48 / 40 = 1.2rem;
                    ?(视口宽度) -> 1rem = (? / 375) * 20 px
                    ?(视口宽度) = document.documentElement.clientWidth
                    1rem = (document.documentElement.clientWidth / 375) * 20 px
                    1rem = (document.documentElement.clientWidth / 750) * 40 px
                    font-size = 1.2rem;
            */
        }
        .tabbar,
        .tabbar-item,
        .tabbar-link {
            height: 100%;
        }
        .tabbar {
            display: flex;
        }
        .tabbar-item {
            flex: 1;
        }
        .tabbar-link {
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;

            font-size: 0.6rem;
        }
        .tabbar-item-active .tabbar-link {
            color: #de181b;
        }
    </style>
</head>
<body>

    <!-- <p style="text-indent: 2em;">
        我是短路
        我是短路
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        我是短路
        我是短路
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    </p> -->

    <div class="tabbar-container">
        <ul class="tabbar">
            <li class="tabbar-item tabbar-item-active">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-home"></i>
                    <span>首页</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-category"></i>
                    <span>分类页</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-cart"></i>
                    <span>购物车</span>
                </a>
            </li>
            <li class="tabbar-item">
                <a href="###" class="tabbar-link">
                    <i class="iconfont icon-personal"></i>
                    <span>个人中心</span>
                </a>
            </li>
        </ul>
    </div>

    <script>
        setRemUnit();

        window.onresize = setRemUnit;

        function setRemUnit() {
            var docEl = document.documentElement;
            var viewWidth = docEl.clientWidth;

            docEl.style.fontSize = viewWidth / 375 * 20 + 'px';
            // docEl.style.fontSize = viewWidth / 750 * 40 + 'px';
            // 1rem = 20px
        }
    </script>
</body>
</html>